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Transcriber’s Note:
The position of the footnote anchor 171 at page 229 is
a guess of the transcriber as the anchor was missing
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THE PROLONGATION
OF LIFE
OPTIMISTIC STUDIES
BY
ÉLIE METCHNIKOFF
SUB-DIRECTOR OF THE PASTEUR INSTITUTE, PARIS
THE ENGLISH TRANSLATION
EDITED BY
P. CHALMERS MITCHELL
M.A., D.SC. OXON., HON. LL.D., F.R.S.
_Secretary of the Zoological Society of London; Corresponding Member
of the Academy of Natural Sciences of Philadelphia_
G. P. PUTNAM’S SONS
NEW YORK & LONDON
The Knickerbocker Press
1908
EDITOR’S INTRODUCTION
Élie Metchnikoff has carried on the high purpose of the Pasteur
Institute by devoting his genius for biological inquiry to the service
of man. Some years ago, in a series of Essays which were intended to
be provocative and educational, rather than expository, he described
the direction towards which he was pressing. I had the privilege of
introducing these Essays to English readers under the title _The Nature
of Man_, a Study in Optimistic Philosophy. In that volume, Professor
Metchnikoff recounted how sentient man, regarding his lot in the world,
had found it evil. Philosophy and literature, religion and folk-lore,
in ancient and modern times have been deeply tinged with pessimism. The
source of these gloomy views lies in the nature of man itself. Man has
inherited a constitution from remote animal ancestors, and every part
of his structure, physical, mental and emotional, is a complex legacy
of diverse elements. Possibly at one time each quality had its purpose
as an adaptation to environment, but, as man, in the course of his
evolution, and the environment itself have changed, the old harmonious
intercourse between quality and circumstances has been dislocated in
many cases. And so there have come into existence many instances of
what the Professor calls “disharmony,” persistences of structures,
or habits, or desires that are no longer useful, but even harmful,
failures of parallelism between the growth, maturity and decay of
physical and mental qualities and so forth. Religions and philosophies
alike have failed to find remedies or efficient anodynes for these
evils of existence, and, so far, man is justified of his historical and
actual pessimism.
Metchnikoff, however, was able to proclaim himself an optimist, and
found, in biological science, for the present generation a hope, or,
at the least, an end towards which to work, and for future generations
a possible achievement of that hope. Three chief evils that hang over
us are disease, old age, and death. Modern science has already made
vast strides towards the destruction of disease, and no one has more
right to be listened to than a leader of the Pasteur Institute when he
asserts his confidence that rational hygiene and preventive measures
will ultimately rid mankind of disease. The scientific investigation
of old age shows that senility is nearly always precocious and
that its disabilities and miseries are for the most part due to
preventable causes. Metchnikoff showed years ago that there exists in
the human body a number of cells known generally as phagocytes, the
chief function of which is to devour intruding microbes. But these
guardians of the body may turn into its deadly enemies by destroying
and replacing the higher elements, the specific cells of the different
tissues. The physical mechanism of senility appears to be in large
measure the result of this process. Certain substances, notably the
poisons of such diseases as syphilis and the products of intestinal
putrefaction, stimulate the activity of the phagocytes and so encourage
their encroachment on the higher tissues. The first business of science
is to remove these handicaps in favour of the wandering, corroding
phagocytes. Specific poisons must be dealt with separately, by
prevention or treatment, and it is well known that Metchnikoff has
made great advances in that direction. The most striking practical
side of _The Nature of Man_, however, was the discussion of the cause
and prevention of intestinal putrefaction. Metchnikoff believes that
the inherited structure of the human large intestine and the customary
diet of civilised man are specially favourable to the multiplication
of a large number of microbes that cause putrefaction. The avoidance
of alcohol and the rigid exclusion from diet of foods that favour
putrefaction, such as rich meats, and of raw or badly cooked substances
containing microbes, do much to remedy the evils. But the special
introduction of the microbes which cause lactic fermentation has
the effect of inhibiting putrefaction. By such measures Metchnikoff
believes that life will be greatly prolonged and that the chief evils
of senility will be avoided. It may take many generations before the
final result is attained, but, in the meantime, great amelioration is
possible. There remains the last enemy, death. Metchnikoff shows that
in the vast majority of cases death is not “natural,” but comes from
accidental and preventable causes. When diseases have been suppressed
and the course of life regulated by scientific hygiene, it is probable
that death would come only at an extreme old age. Metchnikoff thinks
that there is evidence enough at least to suggest that when death comes
in its natural place at the end of the normal cycle of life, it would
be robbed of its terrors and be accepted as gratefully as any other
part of the cycle of life. He thinks, in fact, that the instinct of
life would be replaced by an instinct of death.
Metchnikoff’s suggestion, then, was that science should be encouraged
and helped in every possible way in its task of removing the diseases
and habits that now prevent human life from running its normal course,
and his belief is that were the task accomplished, the great causes of
pessimism would disappear.
In this new volume, _The Prolongation of Life_, the main thesis is
carried further, and a number of criticisms and objections are met.
The latter, so far as they relate to technical details, I need say
nothing of here, as Metchnikoff and his staff at the Pasteur Institute
are the most skilled existing technical experts on these matters, but
I cannot refrain from a word of comment on the brilliant treatment
of the objection to the suggested amelioration of human life that it
considered only the individual and neglected the just subordination
of the individual to society. In the sixth Part of this volume,
Metchnikoff discusses the relation of the individual to the species,
society or colony, from the general point of view of comparative
biology, and shows that as organisation progresses, the integrity of
the individual becomes increasingly important. Were orthobiosis, the
normal cycle of life, attained by human beings, there still would be
room for specialisation of individuals and for differentiation of the
functions of individuals in society, but instead of the specialisation
and differentiation making individuals incomplete throughout their
whole lives, they would be distributed over the different periods of
the life of each individual.
As these lines are intended to be an introduction, not a commentary, I
will now leave the reader to follow the argument in the book itself.
P. CHALMERS MITCHELL.
LONDON, _August, 1907_.
PREFACE
It is now four years since I wrote a volume, the English translation
of which was called _The Nature of Man_, and which was an attempt to
frame an optimistic conception of life. Human nature contains many
very complex elements, due to its animal ancestry, and amongst these
there are some disharmonies to which our misfortunes are due, but also
elements which afford the promise of a happier human life.
My views have encountered many objections, and I wish to reply to some
of these by developing my arguments. This was my first task in this
book, but I have also brought together a series of studies on problems
which closely affect my theory.
Although it has been possible to support my conception by new facts,
some of which have been established by my fellow-workers, others
by myself, there still remain many sides of the subject where it
is necessary to fall back on hypotheses. I have accepted such
imperfections instead of delaying the publication of my book.
Even at present there are critics who regard me as incapable of sane
and logical reasoning. The longer I postpone publication, the longer
would I leave the field open to such persons. What I have been saying
may serve also as a reply to the remark of one of my critics, that my
ideas have been “suggested by self-preoccupation.”
It is, of course, quite natural that a biologist whose attention had
been aroused by noticing in his own case the phenomena of precocious
old age should turn to study the causes of it. But it is equally plain
that such a study could give no hope of resisting the decay of an
organism which had already for many years been growing old. If the
ideas which have come out of my work bring about some modification in
the onset of old age, the advantage can be gained only by those who are
still young, and who will be at the pains to follow the new knowledge.
This volume, in fact, like my earlier one on the “Nature of Man,” is
directed much more to the new generation than to that which has already
been subjected to the influence of the factors which produce precocious
old age. I think that thus the experience of those who have lived and
worked for long can be made of service to others.
As this volume is a sequel to _The Nature of Man_, I have tried as much
as possible to avoid repetition of what was fully explained in the
earlier volume.
Here I bring together the results of work that has been done since the
publication of _The Nature of Man_. Some of the chapters relate to
subjects upon which I have lectured, or which, in a different form,
have been printed before. For instance, the section on the psychic
rudiments of man appeared in the _Bulletin de l’Institut général
psychologique_ of 1904, the essay on Animal Societies was published in
the _Revue Philomatique de Bordeaux et du Sud-Ouest_ of 1904, and in
the _Revue_ of J. Finot of the same year, whilst a German translation
of it appeared in Prof. Ostwald’s _Annalen der Naturphilosophie_. The
chapter on soured milk first appeared as a pamphlet, published in
1905. The substance of my views on natural death was published in June
last in “Harper’s Monthly Magazine” of New York, while the chapter on
natural death in animals appeared in the first number of the _Revue du
Mois_ for 1906.
I have to thank most sincerely the friends and pupils who have helped
me by bringing before me new facts, or other materials; the names
of these will appear in their proper places in the volume. I have
not mentioned by name, however, Dr. J. Goldschmidt, whose continual
encouragement and practical sympathy have made my work much easier.
Finally, my special thanks are due to Drs. Em. Roux and Burnet, and
M. Mesnil, who have been so good as to correct my manuscript and the
proofs of this volume.
É. M.
PARIS, _Feb. 7, 1907_.
CONTENTS
PAGE
EDITOR’S INTRODUCTION v
PREFACE ix
PART I
THE INVESTIGATION OF OLD AGE
I
THE PROBLEMS OF SENILITY
Treatment of old people in uncivilised
countries.—Assassination of old people in civilised
countries.—Suicide of old people.—Public assistance in
old age.—Centenarians.—Mme. Robineau, a lady of 106
years of age.—Principal characters of old age.—Examples
of old mammals.—Old birds and tortoises.—Hypothesis of
senile degeneration in the lower animals 1
II
THEORIES OF THE CAUSATION OF SENILITY
Hypothesis of the causation of senility.—Senility
cannot be attributed to the cessation of the power of
reproduction of the cells of the body.—Growth of the
hair and the nails in old age.—Inner mechanism of
the senescence of the tissues.—Notwithstanding the
criticisms of M. Marinesco, the neuronophags are true
phagocytes.—The whitening of hair, and the destruction
of nerve cells as arguments against a theory of old age
based on the failure of the reproductive powers of the
cells 15
III
MECHANISM OF SENILITY
Action of the macrophags in destroying the higher
cells.—Senile degeneration of the muscular
fibres.—Atrophy of the skeleton.—Atheroma and arterial
sclerosis.—Theory that Old Age is due to alteration
in the vascular glands.—Organic tissues that resist
phagocytosis. 25
PART II
LONGEVITY IN THE ANIMAL KINGDOM
I
THEORIES OF LONGEVITY
Relation between longevity and size.—Longevity and
the period of growth.—Longevity and the doubling
in weight after birth.—Longevity and rate of
reproduction.—Probable relations between longevity and
the nature of the food 39
II
LONGEVITY IN THE ANIMAL KINGDOM
Longevity in the lower animals.—Instances of long life
in sea-anemones and other vertebrates.—Duration of
life of insects.—Duration of life of “cold-blooded”
vertebrates.—Duration of life of birds.—Duration of
life of mammals.—Inequality of the duration of life
in males and females.—Relations between longevity and
fertility of the organism 47
III
THE DIGESTIVE SYSTEM AND SENILITY
Relations between longevity and the structure of
the digestive system.—The cæca in birds.—The
large intestine of mammals.—Function of the large
intestine.—The intestinal microbes and their agency in
producing auto-intoxication and auto-infection in the
organism.—Passage of microbes through the intestinal
wall 59
IV
MICROBES AS THE CAUSE OF SENILITY
Relations between longevity and the intestinal
flora.—Ruminants.—The horse.—Intestinal flora of
birds.—Intestinal flora of cursorial birds.—Duration
of life in cursorial birds.—Flying mammals.—Intestinal
flora and longevity of bats.—Some exceptions to the
rule.—Resistance of the lower vertebrates to certain
intestinal microbes 73
V
DURATION OF HUMAN LIFE
Longevity of man.—Theory of Ebstein on the normal
duration of human life.—Instances of human
longevity.—Circumstances which may explain the long
duration of human life 84
PART III
INVESTIGATIONS ON NATURAL DEATH
I
NATURAL DEATH AMONGST PLANTS
Theory of the immortality of unicellular
organisms.—Examples of very old trees.—Examples of
short-lived plants.—Prolongation of the life of some
plants.—Theory of the natural death of plants by
exhaustion.—Death of plants from auto-intoxication 94
II
NATURAL DEATH IN THE ANIMAL WORLD
Different origins of death in animals.—Examples of
natural death associated with violent acts.—Examples
of natural death in animals without digestive
organs.—Natural death in the two sexes.—Hypothesis as
to the cause of natural death in animals 109
III
NATURAL DEATH AMONGST HUMAN BEINGS
Natural death in the aged.—Analogy of natural death and
sleep.—Theories of sleep.—Ponogenes.—The instinct
of sleep.—The instinct of natural death.—Replies to
critics.—Agreeable sensation at the approach of death 119
PART IV
SHOULD WE TRY TO PROLONG HUMAN LIFE?
I
THE BENEFIT TO HUMANITY
Complaints of the shortness of our life.—Theory of
“medical selection” as a cause of degeneration of the
race.—Utility of prolonging human life 132
II
SUGGESTIONS FOR THE PROLONGATION OF LIFE
Ancient methods of prolonging human life.—Gerokomy.—The
“immortality draught” of the Taoists.—Brown-Séquard’s
method.—The spermine of Poehl.—Dr. Weber’s
precepts.—Increased duration of life in historical
times.—Hygienic maxims.—Decrease in cutaneous cancer 136
III
DISEASES THAT SHORTEN LIFE
Measures against infectious diseases as aiding in the
prolongation of life.—Prevention of syphilis.—Attempts
to prepare serums which could strengthen the higher
elements of the organism 145
IV
INTESTINAL PUTREFACTION SHORTENS LIFE
Uselessness of the large intestine in man.—Case of
a woman whose large intestine was inactive for six
months.—Another case where the greater part of the
large intestine was completely shut off.—Attempts to
disinfect the contents of the large intestine.—Prolonged
mastication as a means of preventing intestinal
putrefaction 151
V
LACTIC ACID AS INHIBITING INTESTINAL PUTREFACTION
The development of the intestinal flora in
man.—Harmlessness of sterilised food.—Means
of preventing the putrefaction of food.—Lactic
fermentation and its anti-putrescent action.—Experiments
on man and mice.—Longevity in races which used
soured milk.—Comparative study of different soured
milks.—Properties of the Bulgarian Bacillus.—Means
of preventing intestinal putrefaction with the help of
microbes 161
PART V
PSYCHICAL RUDIMENTS IN MAN
I
RUDIMENTARY ORGANS IN MAN
Reply to critics who deny the simian origin of
man.—Actual existence of rudimentary organs.—Reductions
in the structure of the organs of sense in man.—Atrophy
of Jacobson’s organ and of the Harderian gland in the
human race 184
II
HUMAN TRAITS OF CHARACTER INHERITED FROM APES
The mental character of anthropoid apes.—Their muscular
strength.—Their expression of fear.—The awakening of
latent instincts of man under the influence of fear 191
III
SOMNAMBULISM AND HYSTERIA AS MENTAL RELICS
Fear as the primary cause of hysteria.—Natural
somnambulism.—Doubling of personality.—Some examples
of somnambulists.—Analogy between somnambulism and
the life of anthropoid apes.—The psychology of
crowds.—Importance of the investigation of hysteria for
the problem of the origin of man 200
PART VI
SOME POINTS IN THE HISTORY OF SOCIAL ANIMALS
I
THE INDIVIDUAL AND THE RACE
Problem of the species in the human race.—Loss
of individuality in the associations of lower
animals.—Myxomycetes and Siphonophora.—Individuality in
Ascidians.—Progress in the development of the individual
living in a society 212
II
INSECT SOCIETIES
Social life of insects.—Development and preservation of
individuality in colonies of insects.—Division of labour
and sacrifice of individuality in some insects 220
III
SOCIETY AND THE INDIVIDUAL IN THE HUMAN RACE
Human societies.—Differentiation in the human
race.—Learned women.—Habits of a bee, Halictus
quadricinctus.—Collectivist theories.—Criticisms by
Herbert Spencer and Nietzsche.—Progress of individuality
in the societies of higher beings 223
PART VII
PESSIMISM AND OPTIMISM
I
PREVALENCE OF PESSIMISM
Oriental origin of pessimism.—Pessimistic
poets.—Byron.—Leopardi.—Poushkin.—Lermontoff.—Pessimism
and suicide 233
II
ANALYSIS OF PESSIMISM
Attempts to assign reasons for the pessimistic conception
of life.—Views of E. von Hartmann.—Analysis of
Kowalevsky’s work on the psychology of pessimism 239
III
PESSIMISM IN ITS RELATION TO HEALTH AND AGE
Relation between pessimism and the state of the
health.—History of a man of science who was pessimistic
when young and who became an optimist in old
age.—Optimism of Schopenhauer when old.—Development of
the sense of life.—Development of the senses in blind
people.—The sense of obstacles 247
PART VIII
GOETHE AND FAUST
I
GOETHE’S YOUTH
Goethe’s youth.—Pessimism of youth.—Werther.—Tendency
to suicide.—Work and love.—Goethe’s conception of life
in his maturity 261
II
GOETHE AND OPTIMISM
Goethe’s optimistic period.—His mode of life
in that period.—Influence of love in artistic
production.—Inclinations towards the arts must be
regarded as secondary sexual characters.—Senile love
of Goethe.—Relation between genius and the sexual
activities 270
III
GOETHE’S OLD AGE
Old age of Goethe.—Physical and intellectual vigour of
the old man.—Optimistic conception of life.—Happiness
in life in his last period 279
IV
GOETHE AND “FAUST”
_Faust_ the biography of Goethe.—The three monologues in
the first Part.—Faust’s pessimism.—The brain-fatigue
which finds a remedy in love.—The romance with
Marguerite and its unhappy ending 283
V
THE OLD AGE OF FAUST
The second Part of _Faust_ is in the main a description
of senile love.—Amorous passion of the old man.—Humble
attitude of the old Faust.—Platonic love for
Helena.—The old Faust’s conception of life.—His
optimism.—The general idea of the play 290
PART IX
SCIENCE AND MORALITY
I
UTILITARIAN AND INTUITIVE MORALITY
Difficulty of the problem of morality.—Vivisection
and anti-vivisection.—Enquiry into the possibility of
rational morality.—Utilitarian and intuitive theories of
morality.—Insufficiency of these 301
II
MORALITY AND HUMAN NATURE
Attempts to found morality on the laws of human
nature.—Kant’s theory of moral obligation.—Some
criticisms of the Kantian theory.—Moral conduct must be
guided by reason 309
III
INDIVIDUALISM
Individual morality.—History of two brothers brought
up in the same circumstances, but whose conduct was
quite different.—Late development of the sense of
life.—Evolution of sympathy.—The sphere of egoism in
moral conduct.—Christian morality.—Morality of Herbert
Spencer.—Danger of exalted altruism 316
IV
ORTHOBIOSIS
Human nature must be modified according to an
ideal.—Comparison with the modification of the
constitution of plants and of animals.—Schlanstedt
rye.—Burbank’s plants.—The ideal of orthobiosis.—The
immorality of ignorance.—The place of hygiene in
the social life.—The place of altruism in moral
conduct.—The freedom of the theory of orthobiosis from
metaphysics 325
THE PROLONGATION OF LIFE
PART I
THE INVESTIGATION OF OLD AGE
I
THE PROBLEMS OF SENILITY
Treatment of old people in uncivilised
countries—Assassination of old people in civilised
countries—Suicide of old people—Public assistance in
old age—Centenarians—Mme. Robineau, a lady of 106 years
of age—Principal characters of old age—Examples of old
mammals—Old birds and tortoises—Hypothesis of senile
degeneration in the lower animals
In the “Nature of Man” I laid down the outlines of a theory of the
actual changes which take place during the senescence of our body.
These ideas, on the one hand, have raised certain difficulties, and, on
the other, have led to new investigations. As the study of old age is
of great theoretical importance, and naturally is of practical value, I
think that it is useful to pursue the subject still further.
Although there exist races which solve the difficulty of old age by
the simple means of destroying aged people, the problem in civilised
countries is complicated by our more refined feelings and by
considerations of a general nature.
In the Melanesian Islands, old people who have become incapable of
doing useful work are buried alive.
In times of famine, the natives of Tierra del Fuego kill and eat the
old women before they touch their dogs. When they were asked why they
did this, they said that dogs could catch seals, whilst old women could
not do so.
Civilised races do not act like the Fuegians or other savages; they
neither kill nor eat the aged, but none the less life in old age often
becomes very sad. As they are incapable of performing any useful
function in the family or in the village, the old people are regarded
as a heavy burden. Although they cannot be got rid of, their death is
awaited with eagerness, and is never thought to come soon enough. The
Italians say that old women have seven lives. According to a Bergamask
tradition, old women have seven souls, and after that an eighth soul,
quite a little one, and after that again half a soul; whilst the
Lithuanians complain that the life of an old woman is so tough that it
cannot be crushed even in a mill. We may take it as an echo of such
popular ideas that murders of old people are extremely common even
in the most civilised European countries. I have been astonished in
looking through criminal records to see how many cases there are of the
murder of old people, specially of old women. It is easy to divine the
motives of these acts. A convict of the Island of Saghalien, condemned
for the assassination of several old persons, declared naïvely to the
prison doctor: “Why pity them? They were already old, and would have
died in any case in a few years.”
In the celebrated novel of Dostoiewsky, “Crime and Punishment,” there
is a tavern scene where young people discuss all sorts of general
topics. In the middle of the conversation a student declares that he
would “murder and rob any cursed old woman without the least remorse.”
“If the truth were told,” he goes on to say, “this is how I look at
the thing. On the one hand a stupid old woman, childish, worthless,
ill-tempered, and in bad health; no one would miss her, indeed she is
a nuisance to everyone. She does not even herself know any reason why
she should live, and perhaps to-morrow death will make a good riddance
of her. On the other hand, there are fresh and vigorous young people
who are dying in their thousands, in the most senseless way, no one
troubling about them, and everywhere the same thing is going on.”
Old people not only run the risk of murder; they very often end their
own lives prematurely by suicide.
They prefer death to a life oppressed by material hardships or burdened
by diseases. The daily papers give many instances of old people who,
tired of suffering, asphyxiate themselves by their charcoal stoves.
The frequency of suicide in the case of the old has been established
by numerous statistics, and the new facts which I now cite do no more
than confirm it. In 1878, in Prussia, amongst 100,000 individuals there
were 154 cases of suicide of men between the ages of 20 and 50, but
295, that is to say, nearly twice as many of men between the ages of 50
and 80. In Denmark, a country in which suicide is notoriously common, a
similar proportion exists. Thus, in Copenhagen, in the ten years from
1886 to 1895, there were 394 suicides of men between 50 and 70. These
figures relate to 100,000 individuals. Of the suicides 36-1/2 per cent.
were those of people in the prime of life, 63-1/2 per cent. those of
the aged.[1]
In such circumstances, it is natural that politicians and
philanthropists have made many attempts to ameliorate the old age of
the poor. In some countries laws have been passed to bring about this.
For instance, a Danish law of June 27th, 1891, established compulsory
aid for the aged, enacting that every person more than 60 years old was
to have the legal right to aid if required. In 1896 more than 36,000
people (36,246) were pensioned under this law, at a cost of nearly
£200,000. In Belgium, the indigent old people are not pensioned until
they reach the age of 65. In France, until recently, the aged poor
could be supported at the public expense only by prosecuting them and
sending them to prison for begging. This state of affairs, however,
ceased with the application of the law of July 15th, 1905, according to
which any French subject without resources, unable to support himself
by work, and either more than 70 years of age, or suffering from some
incurable infirmity or disease, is to receive public assistance.
It has been thought the proper course to make such laws, and to lay
the burden on the general population, without inquiring if it may not
be possible to retard the debility of old age to such an extent that
very old people might still be able to earn their livelihood by work.
Old age can be studied by the methods of exact science, and there may
yet be established some regimen by which health and vigour will be
preserved beyond the age where now it is generally necessary to resort
to public charity. With this object, a systematic investigation of
senescence should be made in institutions for the aged, where there
are always a large number of people from 75 to 90 years old, although
centenarians are extremely rare. I know many institutions for aged
men where, from their first foundation, there has been no case of an
inhabitant reaching the age of 100, and even in similar institutions
for women, although women live to much greater ages than men,
centenarians are very rare. At the Salpêtrière, for instance, where
there is always a large number of old women, it is the rarest chance to
find a centenarian. Opportunity for the study of the extremely aged is
to be found only in private families.
Most of the centenarians whom I have been able to see have been so
defective mentally that all that can be studied in them are the
physical qualities and functions. A few years ago an old woman who
had reached her 100th year was the pride of the Salpêtrière. She was
bedridden and extremely feeble physically and mentally. She replied
briefly when she was asked questions, but apparently without any idea
of what they meant.
Not long ago, a lady who lived in a suburb of Rouen reached her 100th
birthday. The local newspapers wrote exaggerated articles about her,
praising the integrity of her mind and her physical strength. I paid
a visit to her myself, hoping to make a detailed investigation, but
I found at once that the journalists had completely misrepresented
her condition. Although her physical health was fairly good, her
intelligence had degenerated to such an extent that I had to abandon
the idea of any serious investigation.
The most interesting of all the centenarians with whom I have become
acquainted had reached an extremely advanced age, having entered upon
her 107th year. It is about two years ago that a journalist, Monsieur
Flamans, took me to see this Mme. Robineau who lived in a suburb of
Paris. I found her a very old-looking lady, rather short, thin, with a
bent back, and leaning heavily on a cane when she walked. The physical
condition (Mme. Robineau was born on January 12th, 1800), of this
woman of more than 106 years, showed extreme decay. She had only one
tooth; she had to sit down after every few steps, but, once comfortably
seated, she could remain in that position for quite a long time. She
went to bed early and got up very late. Her features displayed very
great age (see Fig. 1), although her skin was not extremely wrinkled.
[Illustration: FIG. 1.—Mme. Robineau, a centenarian. From a photograph
taken on her one hundred and fifth birthday.]
The skin of her hands had become so transparent that one could see
the bones, the blood-vessels, and the tendons. Her senses were very
feeble; she could see only with one eye; taste and smell were extremely
rudimentary; her hearing was her best means of relation with the
external world. None the less, Dr. Löwenberg, a well-known aurist,
had assured himself that her auditory organs showed in a most marked
degree, the usual signs of old age, such as complete insensibility to
high notes and slight deafness for low notes. Dr. Löwenberg attributed
these changes to senile degeneration of the ear which affected more
and more seriously the nervous mechanism although it had caused little
change in the conducting apparatus. Notwithstanding her physical
weakness, Mme. Robineau retained her intelligence fully, her mind
remained delicate and refined and the goodness of her heart was
touching. In contrast with the usual selfishness of old people, Mme.
Robineau took a vivid interest in those around her. Her conversation
was intelligent, connected, and logical. Examination of the physical
functions of this old lady revealed facts of great interest. Dr.
Ambard found that the sounds of the heart were normal, but perhaps a
little accentuated. The pulse was regular, 70 to 84 a minute, and its
tension was normal. The arterial pressure was 17. The lungs were sound.
All these facts testify to her general health. The most remarkable
circumstance was the absence of sclerosis of the arteries, although
such degeneration is usually believed to be a normal character of old
age.
Analysis of the urine, made on several occasions, showed that the
kidneys were affected with a chronic disease, which, however, was not
serious.[2]
Although the sense of taste was weak, Madame Robineau had a fair
appetite. She ate and drank little, but her diet was varied. She
took butcher’s meat or chicken extremely seldom, but ate eggs, fish,
farinaceous food, vegetables, and stewed fruit, and drank sweetened
water with a little white wine, and sometimes, after a meal, a small
glass of dessert wine. The processes of alimentary digestion and
excretion were normal.
It has sometimes been thought that duration of life is a hereditary
property. There was no evidence for this in the present case. Madame
Robineau’s relatives had died comparatively early in life, and a
centenarian was unknown in her family. Her great age was an acquired
character. Her whole life had been extremely regular. She had married a
timber merchant, and had lived for many years in a suburb of Paris in
comfortable circumstances. Her character was gentle and affectionate;
she was thoroughly domesticated, and had been devoted to home life with
very few distractions.
At the age of 106 years, her intelligence suddenly became weak. She
lost her memory almost completely, and sometimes wandered. But her
gentle and affectionate disposition remained unaltered.
The appearance of aged persons is too well known to make detailed
description necessary. The skin of the face is dry and wrinkled and
generally pale; the hairs on the head and the body are white; the back
is bent, and the gait is slow and laborious, whilst the memory is weak.
Such are the most familiar traits of old age. Baldness is not a special
character; it often begins during youth and naturally is progressive,
but if it has not already appeared, it does not come on with old age.
The stature diminishes in old age. As the result of a series of
observations, it has been established that a man loses more than an
inch (3·166 cm.), and a woman more than an inch and a half (4·3 cm.),
between the ages of fifty and eighty-five years. In extreme cases,
the loss may be nearly three inches. The weight also becomes less.
According to Quételet, males attain their maximum weights at the age of
forty, females at that of fifty. From the age of sixty years onwards,
the body becomes lighter, the loss at eighty being as much as thirteen
pounds.
Such losses of height and weight are signs of the general atrophy of
the aged organism. Not merely the soft parts, such as the muscles and
viscera, but even the bones lose weight, in the latter case the loss
being of the mineral constituents. This process of decalcification
makes the skeleton brittle, and is sometimes the cause of fatal
accidents.
The loss of muscular tissue is specially great. The volume diminishes,
and the substance becomes paler; the fat between the fibres is
absorbed, and may disappear completely. Movements are slower, and
the muscular force is abated. This progressive degeneration has been
examined by dynamometrical measurements of the hand and the trunk, and
is greater in males than in females.
The volumes and weights of the visceral organs similarly become
smaller, but the diminution is not uniform.
The old age of lower mammals presents characters similar to those found
in man. I can now give other instances than the case of the old dog
which I described in the “Nature of Man.”
I will first take the case of old elephants, described by a competent
observer. “The general appearance is wretched, the skull being often
hardly covered with skin; there are deep abrasions under the eyes, and
smaller ones on the cheeks, whilst the skin of the forehead is very
often deeply fissured or covered with lumps. The eyes are usually dim,
and discharge an abnormal quantity of water. The margin of the ears,
specially on the lower side, is usually frayed. The skin of the trunk
is roughened, hard, and warty, so that the organ has lost much of its
flexibility. The skin on the body generally is worn and wrinkled; the
legs are thinner than in maturity, the huge mass of muscles being much
shrunken, whilst the circumference, especially just above the feet, is
considerably reduced. The skin round the toe-nails is roughened and
frayed. The tail is scaly and hard, and the tip is often hairless.
[Illustration: FIG. 2.—A Mare, thirty-seven years old.]
[Illustration: FIG. 3.—A White Duck, which lived for more than a
quarter of a century.]
Horses begin to grow old much sooner than elephants. I reproduce (Fig.
2) the photograph of a rare instance of longevity, a mare 37 years
old, which belonged to M. Métaine, in the department of Mayenne. The
skin, bare in places, but elsewhere covered with long hairs, shows
considerable atrophy. The general attitude reveals the feebleness
of the whole body. Many birds, on the other hand, show at similar
ages very slight external change, as may be seen from the photograph
of a duck more than 25 years old (Fig. 3) which belonged to Dr.
Jean Charcot. At a still greater age, as may be seen occasionally
in parrots, the general debility of the body reveals itself in the
attitude, in the condition of the feathers, and in the swelling of the
joints. On the other hand, the oldest reptiles which have been observed
do not differ in appearance from normal adults of the same species. I
have in my possession a male tortoise (_Testudo mauritanica_) given me
by my friends MM. Rabaud and Caullery, and which is at least 86 years
old. It shows no sign of old age, and in all respects behaves like
any other individual of this species. More than 31 years ago it was
wounded by a blow, the traces of which remain visible on the right side
of the carapace (Fig. 4). In the last three years the tortoise lived in
a garden at Montauban, along with two females which laid fertile eggs.
The old male, although, as I have said, probably at least 86 years of
age, was still sexually healthy.
[Illustration: FIG. 4.—An Old Land-tortoise.]
I have borrowed from the interesting volume of Prof. Sir E. Ray
Lankester[3] the figure (Fig. 5) and description of a giant tortoise
from the island of Mauritius, which is probably the oldest of all
living animals. It was brought to Mauritius from the Seychelles in
1764, and has lived since then in the garden of the Governor, and as it
has thus already been 140 years in captivity, its age must be at least
150 years, although we have not exact information. Notwithstanding
this, it shows no signs of old age.
The examples which I have brought together show that often amongst
vertebrates there are some animals the organisms of which withstand
the ravages of time much better than that of man. I think it a fair
inference that senility, the precocious senescence which is one of
the greatest sorrows of humanity, is not so profoundly seated in the
constitution of the higher animals as has generally been supposed. It
is not necessary, therefore, to discuss at length the general question
as to whether senile degeneration is an inevitable event in living
organisms.
[Illustration: FIG. 5.—A Water-tortoise, more than 150 years old.
(After Prof. Sir E. Ray Lankester.)]
I have already shown, in the “Nature of Man,” the difference which
exists between senile degeneration in our own bodies and the phenomena
of senescence amongst Infusoria which, as M. Maupas described, are
followed by a process of rejuvenescence. According to the more recent
results of several investigators, the difference is still greater than
I had supposed. Enriquez[4] has been able to propagate Infusoria to
the 700th generation without any sign of senility being displayed. Here
we are far from the condition in the human race.
R. Hertwig,[5] one of the best observers of the lower animals, has
recently attempted to show that the very simple animalculæ of the genus
_Actinosphærium_ are subject to true physiological degeneration. He
has several times seen cultures of this Rhizopod degenerate, until all
the individuals had died, notwithstanding the presence of abundant
food. Prof. Hertwig attributed this to the “constitution of the
_Actinosphærium_ having been weakened by too great vital activity
at an earlier stage.” I should have thought that it was a much more
natural explanation to suppose that the culture had undergone infection
by one of the contagious diseases which so often destroy cultures of
different kinds of lower animals and plants. As this idea had not
occurred to the observer, he had not searched for parasitic microbes
amongst the granulations which are always present in the body of an
_Actinosphærium_. However this may be, I cannot accept the facts
brought forward by this distinguished German as a valid proof of the
existence of senile degeneration in these lowly creatures.
The facts that I have brought together in this chapter justify the
conclusion that human beings who reach extreme old age may preserve
their mental qualities notwithstanding serious physical decay.
Moreover, it is equally plain that the organism of some vertebrates is
able to resist the influence of time much longer than is the case with
man under present conditions.
II
THEORIES OF CAUSATION OF SENILITY
Hypothesis of the causation of senility—Senility
cannot be attributed to the cessation of the power
of reproduction of the cells of the body—Growth of
the hair and the nails in old age—Inner mechanism of
the senescence of the tissues—Notwithstanding the
criticisms of M. Marinesco, the neuronophags are true
phagocytes—The whitening of hair and the destruction of
nerve cells, as arguments against a theory of old age
based on the failure of the reproductive powers of the
cells
Although it has not been proved that living matter must inevitably
undergo senile decrepitude, it is none the less true that man and his
nearest allies generally exhibit such degeneration. It is therefore
extremely important to recognise the real causes of our senescence.
There have been many hypotheses on the subject, but there are
comparatively few definite facts known.
Bütschli has supposed that the life of cells is maintained by a
specific vital ferment which becomes feebler in proportion to the
extent of cellular reproduction, but I cannot regard this as more than
a pious opinion. The ferment has never been seen, and we do not know
of its actual existence. According to the better-known theory of Prof.
Weismann, old age depends on a limitation in the power of cells to
reproduce, so that a time comes when the body can no longer replace
the wastage of cells which is an inevitable accompaniment of life. As
old age appears at different times in different species and different
individuals, Weismann has concluded that the possible number of cell
generations differs in different cases. He has not found, however,
a solution of the problem as to why multiplication of cells should
cease in one individual, whereas it proceeds much further in other
individuals. Prof. Minot,[6] the American zoologist, has developed
a similar theory, and has employed an exact method to determine the
gradual diminution in the rate of growth of an animal from its birth
onwards. According to him, the power of reproduction of the cells
weakens progressively during life, until a point is necessarily reached
at which the organism, no longer capable of repairing itself, begins to
atrophy and degenerate. Dr. Buehler[7] has recently laid stress upon
this theory.
There is no doubt that cells reproduce much more actively during the
embryonic period. The process becomes slower later on, but, none the
less, continues to display itself throughout the whole period of life.
Buehler attributes the difficulty with which certain wounds heal in the
case of old people to the insufficiency of cellular reproduction. He
thinks in particular that the proliferation of the cells of the skin,
to replace those which are worn off from the surface, becomes less
active with age. According to him, it is theoretically obvious that a
time must come when the replacement of the epidermic cells completely
ceases. As the superficial layers of the skin continue to dry up and
be cast off, it is plain that the epidermis must disappear completely.
Buehler thinks that there must be a similar fate for the genital
glands, the muscles, and all the other organs.
These theoretical considerations, however, are not compatible with
certain well-known facts indicating that there is no general cessation
of the power of cell reproduction in old age. The hairs and the nails,
which are epidermic outgrowths, continue to grow throughout life, their
growth being due to the proliferation of their constituent cells. There
is no sign of any arrest in the development of these structures, even
in the most advanced old age. The reverse is true. It is well known
that the hairs on some parts of the body increase in number and in
length in old people. In some lower races, for instance in the Mongols,
the moustache and the beard grow vigorously in old age, whilst young
people of the same race have only very small moustaches and practically
no trace of beard. So also in white women the fine and almost invisible
down which covers the upper lip, the chin, and the cheeks in the young
may become replaced by long hairs which form a moustache or beard.
Dr. Pohl, a specialist in the growth of hair, has measured the rate of
growth in different circumstances. He has shown that in an old man of
61 the hair on the temple grew 11 mm. in a month; on the other hand,
the hair on the same region in boys of 11 to 15 years old grew in
the same time only from 11 to 12 mm. Plainly, there is no case here
of a progressive diminution of cell-proliferation with age. The same
observer, it is true, has shown that the hair of young men of between
21 and 24 years grew at the rate of 15 mm. a month, whilst in the same
individuals, at the age of 61 years, the rate of growth was only 11
mm.; but this diminution in the rate of growth is only apparent. The
first figure concerned the hair taken from different regions of the
scalp, whilst the second related only to the hair on the temples, and
Dr. Pohl himself has shown that, in the latter region, the hair grows
slower than in other regions. Moreover, in many boys of 11 to 15 years
old, studied by this observer, the rate of growth was always less than
15 mm., and often less even than the 11 mm. recorded in the old man of
61.
I have been able to note that the nails grow even in very old people.
In the case of Mme. Robineau, the centenarian, the nail of the middle
finger of the left hand grew 2-1/2 mm. in three weeks. In the case of a
lady of 32 years old, the corresponding nail grew 3 mm. in two weeks,
the difference being out of all proportion to the enormous difference
in the age. The centenarian’s nails had to be cut from time to time.
Although the hairs of old people grow, they become white, which is a
phenomenon of senile degeneration. Although they increase in length,
the colouring matter in them becomes reduced and finally disappears.
In the “Nature of Man” I described the process by which this blanching
takes place, and which may now be regarded as definitely proved. It is
useful as a means of interpreting the real nature of the process of
senescence. In several published works, I have explained my belief that
just as the pigment of the hair is destroyed by phagocytes, so also the
atrophy of other organs of the body, in old age, is very frequently
due to the action of devouring cells which I have called macrophags.
These are the phagocytes that destroy the higher elements of the body,
such as the nervous and muscular cells, and the cells of the liver and
kidneys. This part of my theory has encountered very strong criticism,
especially with regard to the part played by the macrophags in the
senescence of nervous tissue.
Neurologists in particular, have criticised my interpretation. For
several years M. Marinesco[8] has attacked my theory of the atrophy
of the nerve-cells in old age. In the first place, he has stated that
in old people, and even if these are very old, it is rare to find
phagocytes surrounding and devouring the cells of the brain. In support
of this contention, he has been good enough to send me two preparations
made from the brains of two very old persons. After careful examination
I was convinced that my opponent had been inexact. In the brain of the
two centenarians (one of whom died at the age of 117 years) there were
very many nerve-cells surrounded by phagocytes and in process of being
destroyed by them. It happened, however, that as the sections were very
weakly stained, it was more difficult to observe the facts than in the
preparations upon which I had made my own observations. I have already
recorded this fact in the second and third French editions of the
“Nature of Man.”
Without taking notice of my reply, M. Marinesco has published another
criticism of my theory in an article[9] entitled “Histological
Investigations into the Mechanism of Senility.” In that work, although
he himself had invented the designation “neuronophag” for a phagocyte
that devours nerve-cells, he denies the existence of such a power.
He thinks that nerve-cells atrophy independently of the cells that
surround them. The latter, the so-called neuronophags, only contribute
to the atrophy inasmuch as they press against the nerve-cells and
deprive them of nutrition. He is confident that the constituent parts
of nerve-cells are never found in the neuronophags. There is no
question of phagocytosis, of the existence of cells that devour their
neighbours.
M. Léri has taken a similar view in a Report on the Senile Brain[10]
presented to a recent congress of alienists and neurologists.
According to him “the nuclei which surround some of the atrophying
nerve-cells do not play the part of neuronophags.” In his monograph
“La Neuronophagie,”[11] M. Sand elaborates the same view. He relies
on his observation that “neuronophags are usually either devoid
of protoplasm or display only a very thin layer of it. They never
exhibit protoplasmic outgrowths, and they never have granules in their
cellular bodies (p. 86).” Still more recently MM. Laignel-Lavastine and
Voisin[12] have taken the same view, maintaining that the neuronophags
do not display phagocytosis.
Although I cannot undertake here to give a detailed reply to the
arguments of my critics, I may point out a fallacy that vitiates
their reasoning. The study of the intimate structure of nervous
tissue involves the treatment of that very delicate substance by
numerous active reagents. It is extremely important not to forget the
possibility of alterations which may be produced in the processes of
preparation and which are extremely difficult to avoid. A glance at
the figures given by my critics shows me that the neuronophags in
their preparations had been subjected to violent treatment. When M.
Léri speaks of “the nuclei which surround some of the nerve-cells,”
and M. Sand of “cells without protoplasm,” it is clear that they had
been observing cells destroyed by the processes of the laboratory.
The illustrations in the memoir of M. Marinesco show that in his
preparations, too, the neuronophags had been very greatly altered.
It is well known that nuclei do not exist free in tissues, and that
when they appear devoid of protoplasm, there has been some defect in
the technical methods of preparing them for examination. As a matter
of fact, neuronophags do not consist of nuclei with at the most a
pellicle of protoplasm; like other cells, they have protoplasmic bodies
which, however, are frequently destroyed by the violent processes of
histological preparation.
The arguments of my critics recall to me the words of a medical
student, who, on being asked to describe the microbe of tuberculosis,
said that it was a little red bacillus. The bacillus in question, like
most bacilli, is colourless, but it is usual to stain it so that it
may be visible under the microscope. The student, knowing it only in
particular preparations, had a false idea of its appearance.
In well-made preparations, neuronophags are typical cells with abundant
protoplasm. When they have been preserved by a process that does
not dissolve their contents, they show granules like those found in
nerve-cells.
To study neuronophagy, M. Manouélian,[13] in the laboratory of the
Pasteur Institute in Paris, set himself to improve the technical
methods of preparation. He succeeded in showing first that in the
destruction of nerve-cells that occurs in cases of hydrophobia, the
contents of these cells are absorbed by the surrounding neuronophags.
“My observations on the cerebro-spinal ganglia of human cases of
hydrophobia,” he wrote, “show clearly that the macrophags act as
phagocytes of the nerve-cells.” “Most of the cells in the nerve-ganglia
contain yellow, brown, and black pigmented granules, usually united
in small masses. What becomes of these granulations on the destruction
and disappearance of the nerve-cell? If, as M. Marinesco has it, there
is no phagocytosis by the surrounding cells, but merely a mechanical
interference, then the granules, on the destruction of the nerve-cells
that contained them, should be found lying in the interstitial tissue.
But this does not happen. The granules are ingested by cells which are
true macrophags.”
By the aid of a very delicate mode of preparation, M. Manouélian has
shown that in the case of senile brains the granules of the nerve-cells
are absorbed by neuronophags. I have myself studied M. Manouélian’s
preparations and can testify to the accuracy of his observations (Figs.
6 and 7).
Doubt is no longer possible. In senile degeneration the nerve-cells are
surrounded by neuronophags which absorb their contents and bring about
more or less complete atrophy. It has been supposed that in order to
devour their contents, the neuronophags must penetrate the nerve-cells,
and such an event has rarely been seen. But it is well known, the
phagocytosis of red blood corpuscles being a typical instance, that
to absorb a cell a phagocyte does not necessarily engulf it bodily or
penetrate it, but may gradually denude it of its contents merely by
resting in contact with it.
There has been some discussion as to the condition of nerve-cells which
are on the point of being devoured by neuronophags. It has been noticed
that such cells may display a considerable amount of degeneration
without being devoured, whilst, on the other hand, cells apparently
normal have been found undergoing phagocytosis. As I cannot state
definitely what are the conditions that induce the phagocytosis of
nerve-cells, I shall not attempt a discussion of the problem.
Although the destruction of nerve-cells by neuronophags is a general
occurrence in senile brains, one may conceive of cases where this does
not occur. And so, in old people who have preserved their faculties,
it may well be that the neuronophags have refrained from attacking the
nerve-cells. But as such instances are rare, so also phagocytosis is
usually found in senile brains, and I cannot accept M. Sand’s denial of
its existence, based on his study of two cases.
[Illustration: FIG. 6.]
[Illustration: FIG. 7.
FIGS. 6. & 7.—Two nerve-cells from the cortex of the brain of an old
dog aged fifteen years.
The neuronophags surrounding the nerve-cells contain numerous
granulations.
(From preparations made by M. Manouélian.)]
The general result of my investigation into the criticisms that
have been published on this matter has confirmed me in my belief
that neuronophagy plays a most important part in senescence, and
recent observations that I have made with M. Weinberg have completely
supported this view.
The bleaching of hair and the atrophy of the brain in old age thus
furnish important arguments against the view that senescence is the
result of arrest of the reproductive powers of cells. Hairs grow old
and become white without ceasing to grow. The cessation of the power of
reproduction cannot be the cause of the senescence of brain-cells, for
these cells do not reproduce even in youth.
III
MECHANISM OF SENILITY
Action of the macrophags in destroying the higher
cells—Senile degeneration of muscular fibres—Atrophy
of the skeleton—Atheroma and arterial sclerosis—Theory
that old age is due to alteration in the vascular
glands—Organic tissues that resist phagocytosis
The instances which I have selected in attempting to describe the
mechanism of senescence of the tissues are not the only cases in which
the importance of phagocytosis is evident. The blanching of hair is
due to the destructive agency of chromophags; in atrophy of the brain
neuronophags destroy the higher nerve-cells. In addition to these
instances of phagocytosis, in which the active agents belong to the
category of macrophags, there are many other devouring cells, adrift
in the tissues of the aged, and ready to cause destruction of other
cells of the higher type. The phagocytic action is not so manifest as
in the case of infectious diseases, partly because it is the method of
macrophags to absorb the contents of the higher cells extremely slowly.
The mode of action is well seen in the atrophy of an egg-cell (Fig. 8),
where the surrounding macrophags gradually seize hold of the granules
within it and carry these off. As the process goes on, the ovum becomes
reduced to a shapeless mass, and finally leaves only a few fragments,
or disappears completely. M. Matchinsky[14] has studied the series of
events in my laboratory, and I am myself well assured of the importance
of the action of macrophags in the atrophy of the ovary.
[Illustration: FIG. 8.—Ovum of a Bitch in process of destruction by
Phagocytes, which are full of fatty granules.
(After M. Matchinsky.)]
The phenomena of atrophy in general and of senile decay afford other
cases of tissue destruction in which the phagocytic character of the
process is more modified and obscure than in nerve-cells and ova.
It is well known that progressive muscular debility is an accompaniment
of old age. Physical work is seldom given to men over sixty years
of age, as it is notorious that they are less capable of it. Their
muscular movements are feebler and soon bring on fatigue; their actions
are slow and painful. Even old men whose mental vigour is unimpaired
admit their muscular weakness. The physical correlate of this
condition is an actual atrophy of the muscles, and has for long been
known to observers. More than half a century ago, Kölliker,[15] one of
the founders of histology, devoted some attention to this matter, and
described the senile modification of muscular tissue in the following
words:—“In old age there is a true atrophy of the muscles. The fibres
are much more slender; there are deposited in their substance numerous
yellow or brown granules and many globular nuclei. These nuclei are
frequently arranged in longitudinal series and present such signs of
active division as are found in embryonic tissue.”
Other investigators afterwards made similar observations. Vulpian[16]
and Douaud[17] have stated that a multiplication of nuclei takes places
in the atrophying muscles of the old.
As the senile degeneration of muscular tissue appeared to be important
in my study of the mechanism of senescence, M. Weinberg and I
examined several cases of muscular atrophy in old human beings and
lower animals. We were able to recognise the phenomena observed by
our predecessors. In senile atrophy the muscular fibres contain many
nuclei, and these, increasing rapidly, bring about an almost complete
disappearance of the contractile substance (Fig. 9). The fibres
preserve their striation for a certain time but eventually lose it and
appear to contain an amorphous mass with numerous, rapidly multiplying
nuclei.
[Illustration: FIG. 9.—Degeneration of striated muscle Fibres from the
auricular muscle of a man aged 87 years.
(From a preparation made by Dr. Weinberg.)]
The investigators who had recorded these facts thought of them only as
curious. It is plain, in the first place, however, that this remarkable
and rapid multiplication is a proof that senile atrophy is not due to
failure of cell proliferation, although the latter has frequently been
suggested as the mechanism of senescence. In muscular atrophy, cell
multiplication, so far from failing, greatly increases. We may add
muscular atrophy to the blanching of hair and the decay of nerve-cells
as another instance showing that senile degeneration is not the result
of cells ceasing to be able to multiply. Just as in the atrophy
of the brain there is an increase in the volume of neuroglœa,
the substance in which the neuronophags are found, so also in the
atrophy of the muscles there is an increase of muscular nuclei. Along
with the increase of nuclei, however, there is an increase of the
protoplasmic substance of the fibres known as sarcoplasm. The latter
replaces the myoplasm, the specific striated substance of muscles, by
a process which must be regarded as parallel with phagocytosis. In a
normal muscle the two substances and the sarcoplasmic nuclei are in
equilibrium, but in old age the sarcoplasm and its nuclei increase at
the expense of the myoplasm. The equilibrium is destroyed with the
result that the muscular power is weakened. In these conditions the
sarcoplasm acts phagocytically with regard to the myoplasm, just as the
chromophag becomes the phagocyte of the pigment of the hair, or the
neuronophag devours the nerve-cell.
The investigation of other cases of muscular atrophy, as, for instance,
that of the caudal muscles of frog-tadpoles, confirms the significance
of the process that I have observed in old age. In the two cases, what
takes place is the destruction of the contractile material of the
muscles by myophags, a special kind of phagocyte.
It is one of the curiosities of senile atrophy that whilst there is
hardening or sclerosis of so many organs, the skeleton, the most
solid part of our frame-work, becomes less dense, so that the bones
are friable, the condition often leading to serious accidents in old
people. The bones become porous, and lose weight. It is difficult to
believe that macrophags, although they destroy softer elements such
as nerve-cells or muscle fibres, can be able to gnaw through a hard
material like bone impregnated with mineral salts. As a matter of fact,
the mechanism of bone atrophy must be placed in a different category
from the phagocytosis of other organs. It is brought about, however,
by the agency of cells very like some of the macrophags. These cells
contain many nuclei, and are known as osteoclasts. They form round
about the bony lamellæ and lead to their destruction, but are incapable
of breaking off fragments of bone and dissolving them in their
interiors. Although the intimate mechanism of this destructive action
is not thoroughly understood, it seems probable that the cells secrete
some acid which softens bone by dissolving the lime salts. The process
can be observed in the different varieties of caries of the bone, and
in the bony atrophy of old age as is represented in Fig. 10.
By the action of the osteoclasts, which themselves are macrophags, part
of the lime in the skeleton is dissolved during old age and passes into
the general circulation. This is probably a source of the lime which is
deposited so readily in the different tissues of old people. Whilst the
bones become lighter, the cartilages become bony, the inter-vertebrate
discs in particular becoming impregnated with salts, so that the
well-known senile malformation of the backbone is produced.
[Illustration: FIG. 10.—Destruction by osteoclasts of bony matter in
the sternum of a man aged 81 years.
(From a preparation made by Dr. Weinberg.)]
As a result of this displacement of lime in old age, the blood-vessels
become modified in a distinctive fashion. Atheroma of the arteries
is not invariable in old people, but it occurs extremely frequently.
In this form of degeneration, lime salts are deposited in the walls
of the cells, so that they become hard and friable. Several others,
among whom I may mention Durand-Fardel and Sauvage, have laid stress
on the coincidence of atheromatous lesions of the arteries and senile
degeneration of the bones. The relations between the two alterations
are very evident in the skull; the meningeal artery becomes sinuous and
atheromatous, and the grooves on the inner side of the bones of the
skull in which it runs, flatten out, and become larger because of other
malformations.[18]
There is no disharmony in the nature of old people so striking as this
transference of the lime salts from the skeleton to the blood-vessels,
producing as it does a dangerous softening of the former, and a
hardening of the latter that interferes with their function of carrying
nutrition to the organs. It is the manifestation of an extraordinary
disturbance of the properties of the cells that compose the body. The
atheromatous condition of the arteries is closely linked with arterial
sclerosis, an affection which is very common, although not constant,
in the aged. The whole question of these vascular alterations is
extremely complex, and before it can be cleared up, a number of special
investigations must be made.
Probably diseases of the arteries of different kinds, and arising from
different causes, are grouped under the terms atheroma and sclerosis.
In some cases the lesions are inflammatory and are due to the poisons
of microbes. An example of such an origin is the case of syphilitic
sclerosis, in which the specific microbes (spirilla of Schaudinn) lead
to precocious senescence. In other cases the arteries show phenomena of
degeneration resulting in the formation of calcareous platelets which
interfere with the circulation of the blood.
Investigations which have been made in recent years have led to very
interesting results concerning the origin of atheroma of the arteries.
In most cases, attempts to produce such lesions of the arteries by
experimental methods have not succeeded, but M. Josué[19] has been
able to produce true arterial atheroma in rabbits by injecting into
them adrenaline, the secretion of the supra-renal capsules.
This experiment has been repeated many times and is now well known.
Later on, M. Boveri[20] obtained a similar result by injecting
nicotine, the poison of tobacco. It is obvious, therefore, that amongst
the arterial diseases which play so great a part in senescence, some
are chronic inflammations produced by microbes, whilst others are
brought about by poisons introduced from without.
It is easy to understand, therefore, why these diseases of the arteries
are not always present in old age, although they are very common.
The part played by the secretion of the supra-renal glands in the
production of arterial disease has brought renewed attention to a
theory which supposed that certain glandular organs in the body play
a preponderating part in senile degeneration. Dr. Lorand[21] in
particular has argued that “senility is a morbid process due to the
degeneration of the thyroid gland and of other ductless glands which
normally regulate the nutrition of the body.” It has long been noticed
that persons affected with myxodema, as a result of the degeneration
of the thyroid gland, look like very old people. Everyone who has seen
the cretins in Savoy, Switzerland, or the Tyrol, must have noticed the
aged appearance of these victims, although very often they are quite
young. The condition of cretinism, with its profound bodily changes,
is the result of degeneration of the thyroid gland. On the other hand,
it is well known that in old people the thyroid and the suprarenals
frequently show cystic degeneration. It is quite probable, therefore,
that these so-called vascular glands have their share in producing
senility. Many facts show that they destroy certain poisons which have
entered the body, and it is easy to see that, if they have become
functionless, the tissues are threatened with poisoning. It does not
follow, however, that their action in producing senility is exclusive,
or even preponderating. M. Weinberg, at the Pasteur Institute, made
special investigations on this point, and found that the thyroid gland
and the supra-renal capsules were almost invariably normal in old
animals (cat, dog, horse), although the latter showed unmistakable
signs of senility. Similarly in an old man of 80 years, who died from
pneumonia, the thyroid gland was quite normal.
It must not be forgotten that the aged very often die from infectious
diseases such as pneumonia, tuberculosis, and erysipelas. In these
diseases the vascular glands generally, and the thyroid gland in
particular, are very often affected, with the result that what is due
to infection has been set down as a symptom of old age.[22]
Although the appearance of patients from whom the thyroid gland has
been removed, or in whom it has degenerated spontaneously, recalls
that of old people, it is possible to exaggerate the similarity. In
the masterly accounts of such unfortunates, recently compiled by
the well-known surgeon Kocher[23] there are many points which are
characteristic, without being typical, of old people.
Oedema of the skin which characterises thyroid patients is by no
means usual in old age. The loss of hair, normal in the patients, is
not a character of old age. In myxedematous women, menstruation is
very active; it ceases in old women. The great muscular development of
myxedematous patients distinguishes them from old people.
Physiological investigation does not support the existence of any
strong affinity between old age and affection of the thyroid gland. It
is known that removal of the thyroid is followed by cachexia only in
young subjects, MM. Bourneville and Bricon[24] having shown that the
tendency to cachexia after extirpation of the thyroid ceases almost
abruptly at the age of thirty. That age may be taken as the limit of
youth, of the time when growth is vigorous and the function of the
thyroid most active. Cases of cachexia, where the thyroid gland has
been removed in old persons from fifty to seventy, are very rare.
Rodents (rats, rabbits) support the removal of the thyroid extremely
well, without signs of cachexia, although these are normally
short-lived creatures. According to Horsley[25] extirpation of the
thyroid is not followed by cachexia in birds or rodents and is followed
by it only very slowly in ruminants and horses; it produces the
condition invariably but slightly in man and monkeys and extremely
seriously in carnivora. If this series be compared with the information
given in the next section of this volume on the relative ages which
the animals in question attain, it will be seen that there is no
correspondence.
In short, whilst I do not deny that the vascular glands may take a
share in the causation of senility, in so far as they are destroyers
of poisons, I cannot agree with the theory of Dr. Lorand.
[Illustration: FIG. 11.—Testis tissue from a dog aged twenty-two years.
(From a preparation made by Dr. Weinberg.)]
I think it indubitable that in senescence the most active factor is
some alteration in the higher cells of the body, accompanied by a
destruction of these by macrophags which gradually usurp the places of
the higher elements and replace them by fibrous tissue. Such a process
affects the organs of secretion (kidneys), the reproductive organs, and
in a modified form the skin, the mucous membranes, and the skeleton.
The testes are amongst the organs which resist invasion by macrophags.
I have already given an example (“The Nature of Man,” p. 98) of an old
man of 94 in whom active spermatozoa were produced. I know of a similar
case, the age being 103 years. Such cases are not rare, and not only
in old men, but in old animals, the testes continue to be active. Dr.
Weinberg and I have investigated these organs in a dog which died at
the age of 22 years after several years of pronounced senility. Many of
the organs of the animal exhibited serious invasions by macrophags but
the testes were extremely active, the cells being in free proliferation
and producing abundant spermatozoa (Fig. 11). In harmony with this
condition of the sexual organs, the sexual instincts of the animal
remained normal. We have investigated another dog which died at the age
of eighteen years. In this case the testes were cancerous and there was
no possibility of the production of spermatozoa. None the less, this
dog although markedly senile (Fig. 12) still showed sexual instincts
until shortly before it died.
[Illustration: FIG. 12.—An old dog, aged eighteen years.]
It is manifest that the tissues do not invariably degenerate in
old age, nor do all the organs that are modified in old age show
destruction by phagocytes and replacement by connective tissue. Organs
which produce phagocytes, such as the spleen, the spinal marrow and
the lymphatic glands, certainly show traces in old age of fibrous
degeneration but remain sufficiently active to produce macrophags which
destroy the higher cellular elements of the body. I have frequently
noticed cell division in such organs, and as an example may give the
case of the bone marrow taken from a man of 81 years (Fig. 13).
The eye is an organ that is modified in old age without the action of
macrophags. Cataract and the senile arc which appears as a milky ring
at the edge of the cornea are frequent in old age. These modifications
are due to impregnation of the parts affected by fatty matter which
makes them opaque. This deposition of fat[26] has been attributed to
defective nutrition. In most organs such fatty degeneration is followed
by phagocytosis, but the cornea and the crystalline lens are exempt
from this consequence for anatomical reasons. Most organs possess in
addition to their higher elements a constant source of macrophags.
Such a source of phagocytosis is the neuroglœa in nervous tissues,
the sarcoplasm in muscular tissues; the bones contain osteoclasts and
the liver and the kidneys are readily invaded by phagocytes from the
blood. The lens and the cornea have no cells that are able to become
macrophags.
[Illustration:
FIG. 13.—Bone marrow from the sternum of a man aged
eighty-one years.
(From a preparation made by Dr. Weinberg.)]
Some infectious diseases bring about precocious senility. A syphilitic
child is “a miniature old man, with wrinkled face, skin dull and
discoloured and flabby and hanging in folds as if it were too
large.”[27] In such a case the active agent is the microbe of syphilis
which has poisoned the child on the breast of its mother. It is no
mere analogy to suppose that human senescence is the result of a slow
but chronic poisoning of the organism. Such poisons, if not completely
destroyed or eliminated, weaken the tissues, the functions of which
become altered or enfeebled, so that, amongst other changes, there
is deposition of fatty matter. The phagocytes resist the influence of
invading poisons better than any of the other cells of the body and
sometimes are stimulated by them. The general result of such conditions
is that there comes to be a struggle between the higher cells and the
phagocytes in which the latter have the advantage.
The answer to the question as to whether our senescence can be
ameliorated must be approached from several points of view. This course
I shall now follow.